Centrifugal pumps installed in aquaria often run for years day and night. In view of these operating times, it is important, even when smaller pumps are involved, how much electrical power the electric motor uses. Unfavourable ratios of friction in the transmission of power between the electric motor and the impeller can impair the efficiency of a pump to such an extent that a greater electrical power input is required for the same delivery.
Friction in the drive not only impairs the efficiency of the pump but also reduces its life. This is of special importance for a unit which is in continuous operation. In addition, friction increases the noise level produced by the pump. However, it is imperative that aquarium pumps, which are often operated in inhabited places, should run with a maximum of silence.
It follows that a maximum of attention must be given to the moving parts of such centrifugal pumps. On the other hand, for reasons of cost, it should be possible to manufacture the pump to a considerable extent from plastics material and by the injection-moulding process. Finally, it must be easy to assemble the individual parts and just as easy to take them apart for maintenance or cleaning purposes.